Interstellar Gas in the Local Chimneys

Abstract

ABSTRACTWe present ultraviolet absorption observations of four nearby (d < 250 pc) DA white dwarfs using spectral data (R ∼ 15 km s-1) obtained with the NASA HST Cosmic Origins Spectrograph (1150–1700 Å) and the Far Ultraviolet Spectroscopic Explorer (912–1170 Å). Two of these targets (WD2321 - 549 and WD2124 - 224) sample gas along the Southern Local Chimney sight line, while WD1040 + 492 samples gas within the Northern Local Chimney and the sight line toward WD2257 - 073 samples gas located entirely within the central confines of the Local Interstellar Cavity. We have fit the numerous high and low ion interstellar absorption-line profiles with theoretical models in order to determine the velocity and ion column densities of the sight-line gas clouds. Using these data we have derived element abundances relative to that of (assumed undepleted) sulfur for each of the four sight lines. We find that the 89 pc sight line toward WD2257 - 73 reveals a pattern of element depletion associated with interstellar gas located within the inner Local Cavity that is greater than those derived for the other three sight lines that sample gas within the two Local Chimney features. The sight lines toward WD2124 - 224 and WD2321 - 549, which sample gas along the Southern Local Chimney, show patterns of element depletion that are greater than that derived for the Northern Local Chimney sight line toward WD1040 + 492. Although our sight line sample is small, these data seem to indicate that the interstellar gas located along both local chimneys may be chemically different from gas within the central regions of the Local Cavity. This may indicate that Local Chimney gas has a different physical history and origin from the interstellar gas located within the inner Local Cavity.